Using a small ALOX cup wheel instead of a carbide cutter on steel?

[RCaffin]

I am making up some tooling jigs out of steel. That works, but there are still machining marks on the steel. I would love it to look 'ground'.
So I have JUST started using a small (40 mm?) Norton alox cup wheel as a mounted point in place of the 10 mm cutter, but I have only made a few passes so far. I have not done any serious metal removal yet.
I know from experience that trying to use a 150 mm alox cup wheel can be tricky as the drag is extremely high when most of the rim is engaged, although it may be that I was taking too big a bite at the time.
Before you ask, yes, I KNOW a proper surface grinder would be far far better for this, but I don't have one. On the other hand, I do have a fairly solid CNC.
So, question: has anyone else done this?
Cheers
Roger

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[RCaffin]

Well, the idea works fine with a small Norton cup wheel.
Operating conditions: 2,600 RPM, Feed 500 mm/min, 5 mm overlap between passes, 0.004 mm DoC (that's 4 microns).

but of course there are some traps for the beginners (me). (Please note: I do not have a surface grinder, so that idea is out.)

Trap 1: do NOT be too hungry! You might regard a 0.100 mm Doc as being very small for a cutter. Well, when grinding like this I find a 0.004 mm cut is large enough, and my machine is fairly robust.

Trap 2: a large diameter cup wheel creates a lot of contact area, and that creates a lot of drag. It is not hard to stall the spindle with this drag. Roughs up the surface something awful when you do that too. A small cup wheel is more 'usable'.

Trap 3: do not operate dry. You NEED a liquid there: not a lot, but certainly not dry. Kerosene or water is recommended by some. I use a pulsed kero/olive oil mix with an air blast, and that was very visibly better than running dry, even with the very small quantities involved.

Trap 5: a tilt from end to end (left to right) of 0.1 mm in the part shown would not matter for a milling cutter going across the span. Trivial. But when the DoC is 4 microns, a tilt of 100 microns can destroy ... something! Hint: a preliminary pass with a carbide cutter will give a level start.


In this case I had removed the part after milling it and then replaced it, but what with dust or whatever there was a 10 - 15 micron tilt from side to side. You can see how the right hand side is all beautiful and shiny, while some grotty machining marks (milling cutter) are still visible on the left. The marks don't actually matter much as they are below the ground surface, but they do show why I wanted something better.
Why did the marks appear this time? I have no idea. Maybe the HSS cutter was not sharp enough?
Why didn't I redo the milling? Because the marks were an excellent guide to how the grinding was going.

Has anyone else played this game?
Cheers
Roger

[mactec54]

Well, the idea works fine with a small Norton cup wheel.
Operating conditions: 2,600 RPM, Feed 500 mm/min, 5 mm overlap between passes, 0.004 mm DoC (that's 4 microns).

but of course there are some traps for the beginners (me). (Please note: I do not have a surface grinder, so that idea is out.)

Trap 1: do NOT be too hungry! You might regard a 0.100 mm Doc as being very small for a cutter. Well, when grinding like this I find a 0.004 mm cut is large enough, and my machine is fairly robust.

Trap 2: a large diameter cup wheel creates a lot of contact area, and that creates a lot of drag. It is not hard to stall the spindle with this drag. Roughs up the surface something awful when you do that too. A small cup wheel is more 'usable'.

Trap 3: do not operate dry. You NEED a liquid there: not a lot, but certainly not dry. Kerosene or water is recommended by some. I use a pulsed kero/olive oil mix with an air blast, and that was very visibly better than running dry, even with the very small quantities involved.

Trap 5: a tilt from end to end (left to right) of 0.1 mm in the part shown would not matter for a milling cutter going across the span. Trivial. But when the DoC is 4 microns, a tilt of 100 microns can destroy ... something! Hint: a preliminary pass with a carbide cutter will give a level start.


In this case I had removed the part after milling it and then replaced it, but what with dust or whatever there was a 10 - 15 micron tilt from side to side. You can see how the right hand side is all beautiful and shiny, while some grotty machining marks (milling cutter) are still visible on the left. The marks don't actually matter much as they are below the ground surface, but they do show why I wanted something better.
Why did the marks appear this time? I have no idea. Maybe the HSS cutter was not sharp enough?
Why didn't I redo the milling? Because the marks were an excellent guide to how the grinding was going.

Has anyone else played this game?
Cheers
Roger

Yes many times I have a 6" Diamond and a Borazon wheel set up to do this, I have a 18 x 8 surface grinder, but some times it is just not large enough to do some parts

Coolant is always a good idea when grinding

[RCaffin]

6" diamond wheel? That's a very big diameter relative to the work volume of my machine. Do you find it gives a lot of drag?
For the moment my diamond and CBN wheels are restricted to the T&C.

Cheers
Roger

[mactec54]

6" diamond wheel? That's a very big diameter relative to the work volume of my machine. Do you find it gives a lot of drag?
For the moment my diamond and CBN wheels are restricted to the T&C.

Cheers
Roger

Any time a cup wheel is used like this it will have some drag, you want to use as coarse a grit as you can, what I have done with the type of wheel that you are using is to cut it into segments, around the diameter of the wheel just a 1/8 or so deep, then balance and dress it, can make a big difference as to how it works, so the wheel when you look at it will have teeth on it, you can mount the wheel on your 4th axes to get a perfect job or you can just try and cut it out by hand

[Eldon_Joh]

Sort of hard to imagine you could stall your spindle without also destroying that cup wheel, do you have one of those 24,000 rpm spindles?

Anyhow, typical 8" aluminum oxide wheel is typically used in a 3500 rpm bench grinder, same surface speed would be 18,000 rpm for your 40mm cup wheel. cup wheels probably aren't as strong, so check the maximum rpm from the manuf.

If you want to keep the surface speed low so that you don't make any sparks, then you might be able to go as fast as 4500 rpm. i have a 6 inch aluminum oxide wheel on a 1200 rpm motor and depending on the feed pressure, grinding steel cutting tools doesn't make any significant sparks.

[RCaffin]

Hi Mactec
Photos - we need photos! And details of how you segmented the wheel too, please!

Hi Eldon
Manual mill, 1,800 RPM max. I think the belt started to slip, but I acted very quickly. Anyhow, I can't get those revs, so I have to make do with what I have. It worked, all very quiet and low on excitement, and a nice finish.

Cheers
Roger